1. Field of the Invention
This invention relates generally to the application of batteries and battery charge indicators used in powering systems such as, but not limited to, underwater applications such as marine seismic exploration. More specifically, this invention relates to a battery-powered circuit with two batteries, either of which is capable of handling system power requirements, and a circuit that furnishes an external visual indication of battery health for use with towed streamer cable retrievers.
2. Description of the Prior Art
While conducting offshore seismic surveys for oil and gas deposits, it is customary to tow streamer cables, often three to ten kilometers in length, beneath the surface and astern of a ship. As many as twelve of these streamer cables can be towed simultaneously. Each cable contains multiple hydrophones as well as associated electronics and other sensors required in the exploration process and can cost over one million dollars. These streamers are constructed using semi-plastic material or oil-filled plastic tubing. They are typically five to seven centimeters in diameter.
While towing long streamer cables, a number of hazards exist that can cause damage or loss to any overboard equipment. Under-water obstructions, trawlers and extreme sea conditions all pose a threat to the streamer cables. It is important that an automatic floatation and recovery system be employed at all times to keep the entire cable afloat if an accident occurs which causes the cable to sink.
FIG. 1 of the attached drawings shows a prior art system. The safety of a streamer cable (12) relies on a floatation system referred to as a “retriever” (10). Retrievers (10) are attached along the length of the streamer cable (12) at intervals of about three hundred meters. The retrievers are attached to the streamer cables by collars (14) which allow the retriever to freely rotate about the cable. The retriever often has a removable tailpiece (15) for access to internal components. As shown in FIG. 2, each retriever (10) is an independent system that includes a compressed gas canister (16), an inflatable floatation bag (18), an electrically actuated detonator (20) designed to rupture the seal of the gas canister (16) for releasing compressed gas into the flotation bag (18) to inflate it, a pressure switch (22) which senses seawater pressure, and a battery (24) (See FIG. 4) which powers the detonator (20) upon closure of the pressure switch (22).
If the streamer cable sinks to a depth of about forty-eight meters, the pressure switch (22) actuates, thereby directing electric current from the battery (24) to the detonator (20), also known as a squib, which pierces the seal of the gas canister (16). The pressurized gas inflates the floatation bag (18) to provide the buoyancy necessary to lift the cable (12) to the surface for recovery. An actuated retriever is shown in FIG. 3. The gas-filled floatation bag (18) causes the cable (12) to rise to the surface.
Additional background information concerning cable buoyancy is provided in U.S. Pat. No. 5,404,339 issued to Cole, on Apr. 4, 1995, which is incorporated in its entirety herein by reference. Other methods for maintaining buoyancy within a streamer cable have been developed. Examples include: U.S. Pat. No. 6,019,652, entitled Buoyancy Adjustment, issued Feb. 3, 2000 to Neilson, et al.; U.S. Pat. No. 6,142,092, entitled Depth Control Device, issued Nov. 7, 2000 to Copeland; U.S. Pat. No. 6,188,646, entitled Hydrophone Carrier, issued Feb. 13, 2001 to Luscombe, et al.; and U.S. Pat. No. 6,239,363, entitled Variable Buoyancy Cable, issued May 29, 2001 to Wooters.
As illustrated in FIG. 4, prior art retrievers contain only one battery (24) and have no means to monitor the battery charge or “health” by an external inspection. If the battery (24) becomes discharged for any reason prior to retriever activation, a catastrophic loss can occur if the cable sinks. Some prior art retriever designs preferably use a lithium cell for the single battery (24). However, it is difficult to determine the capacity of a given lithium cell using voltage measurements alone. A method which simply allows a user to verify that a battery cell within a sealed enclosure has ample charge to function is desirable. Additionally, a redundant battery source is desirable, because a single battery may pass the most recent visual inspection yet fail while the retriever is in use.
Dual battery circuits are known. For example, U.S. Pat. No. 4,090,122 issued to Hoinski discloses an automotive dual battery system with logic means to determine to which battery the load should be switched. U.S. Pat. No. 5,235,979 issued to Adams and U.S. Pat. No. 5,372,605 issued to Adams et al. each disclose a dual battery system with a monitoring circuit for use in implantable defibrillators. U.S. Pat. No. 5,549,984 issued to Dougherty describes a control and indicator circuit for a dual battery system.
3. Identification of Objects of the Invention
A primary object of the invention is to provide a redundant cell battery power supply with a combined cell health visual indicator which notifies the user that at least one of the two battery cells has been depleted.
Another object of the invention is to provide an external, visual, bright and essentially continuous indication of the condition of the redundant batteries which are sealed in a watertight enclosure.